1. Field of the Invention
The present invention relates to a fuel injection valve for the cylinder injection of fuel which injects fuel directly into the combustion chamber of an internal combustion engine.
2. Description of the Related Art
An example of a conventional (but not prior art) fuel injection valve 1 for the cylinder injection is shown in FIGS. 2 to 4.
FIG. 2 shows a cross-sectional view of a fuel injection valve 1 for the cylinder injection. In the figure, the tip of the fuel injection valve 1 for the cylinder injection is inserted into an injection valve socket 6 in a cylinder head 5 in an internal combustion engine. A flange portion 2a of a housing 2 is held by a generally plate-shaped fork 28, and the fuel injection valve 1 for the cylinder injection is attached to the cylinder head 5 by securing the fork 28 to the cylinder head 5 by means of a bolt 29. A seal is formed between the cylinder head 5 and the fuel injection valve 1 for the cylinder injection by means of a corrugated washer 160.
The fuel injection valve 1 for the cylinder injection comprises the above housing 2 and a valve assembly 3 supported by one end of this housing 2 by a fastening means such as caulking.
The valve assembly 3 comprises: a stepped, hollow, cylindrical valve main body 9 which has a small-diameter cylinder portion 7 and a large-diameter cylinder portion 8; a valve seat 11 which has a fuel injection hole 10 and is secured to the tip of the central hole within the valve main body 9; a needle valve 12 which is a valve body which is moved in and out of contact with the valve seat 11 by means of a solenoid assembly 26 to close and open the fuel injection hole 10; and a swirler body 13 which guides the needle valve in the axial direction and also imparts a swirling motion to the fuel as it is about to flow radially inward into the fuel injection hole 10 of the valve seat 11.
The solenoid assembly 26, which comprises a coil 27, is disposed within the housing 2. A core 33 which, together with an armature 30 and the housing 2, defines a magnetic circuit is disposed within the solenoid assembly 26. Within the core 33, there are cylindrical bores 33a and 33b of different diameter. A spring 31 which pushes the needle valve 12 against the valve seat 11 and a hollow cylindrical rod 32 which adjusts the tension in the spring 31 are disposed in the cylindrical bore 33a, and a fuel filter 34 is disposed in the cylindrical bore 33b.
In addition, a delivery pipe O-ring 35 is disposed around the outside of one end of the core 33 between backup rings 36, 37 to prevent fuel which is supplied to the fuel injection valve 1 for the cylinder injection from the high-pressure fuel pump, which is not shown, via the inside of the delivery pipe 4 from leaking between the core 33 and the delivery pipe 4.
A bush 38, which has a thin cylindrical wall 38a, is disposed around the outside of the other end of the core 33 adjacent to the solenoid assembly 26. An external O-ring 40 is disposed around the outside of this thin cylindrical wall 38a to form a seal between the housing 2 and the thin cylindrical wall 38a of the bush 38, and an internal O-ring 41 is disposed around the inside of the thin cylindrical wall 38a to form a seal between the core 33 and the thin cylindrical wall 38a of the bush 38, so that fuel is prevented from seeping into the coil 27. Also, a spacer 39 is disposed on the opposite side of the external O-ring 40 and internal O-ring 41 from the coil 27 to position the external O-ring 40 and the internal O-ring 41 in the axial direction.
FIG. 3 is an enlarged sectional view showing the vicinity of the swirler body 13, which constitutes part of the valve assembly 3, and FIG. 4 is a view of the swirler body 13 from the direction of an arrow X of FIG. 3. In FIGS. 3 and 4, the swirler body 13 is a hollow, generally-cylindrical member which has a central bore 15 which surrounds and centrally supports the needle valve 12 which is a valve member, so that it can slide in the axial direction, and the swirler body 13 comprises: a first end surface 16 which comes into contact with the valve seat 11 when assembled in the valve assembly 3; a second end surface 17 at the opposite end from the valve seat 11; and an outer surface 19 between these two end surfaces which comes into contact with a curved inner surface 18 of the valve main body 9.
The second end surface 17 of the swirler body 13 comes into contact with and is supported around its circumference by a shoulder portion 20 on the curved inner surface 18 of the valve main body 9, and has passage grooves 21 formed therein which extend radially and allow fuel to flow from the inner portion to the radially outer portion of the second end surface 17.
A plurality of flat surfaces which extend in the axial direction and are spaced evenly around the circumference are formed in the outer surface 19 of the swirler body 13, and as a result, in the outer surface 19 there are formed: a plurality of curved outer surface portions which come into contact with the curved inner surface 18 of the valve main body 9 and regulate the position of the outer surface 19 with respect to the valve main body 9; and channel portions 23 which are flat surfaces disposed between these curved outer surface portions and, together with the curved inner surface 18, defines axial channels 22 for the fuel. These axial channels 22 are the spaces between the curved inner surface 18 of the valve main body 9 and the flat channel portions 23, and so they have a substantially D-shaped cross-section (shaded portion in FIG. 4).
In the first end surface 16 of the swirler body 13 which faces the valve seat 11, there are disposed: an inner annular groove 24 of a prescribed width formed on the inside edge where the first end surface 16 meets the central bore 15; and rotation grooves 25 which are connected at one end to the channel portions 23 of the outer surface 19, extend generally radially inwards from there at a tangent to the inner annular groove 24, and are connected at a tangent to the inner annular groove 24 at the other end.
In the fuel injection valve 1 for the cylinder injection constructed in this way, the fuel in the delivery pipe 4 passes through the fuel filter 34, through the cylindrical bore in the rod 32, through the cylindrical bore 33a in the core 33, and through the cylindrical bore in the armature 30, then passes through a two-sided cut portion 12a on the needle valve 12, through an opening in a U-shaped stopper 42, and around a four-sided cut portion 12b on the needle valve 12, and is fed as far as the swirler body 13.
When electricity is supplied to the coil 27, magnetic flux is generated in the magnetic circuit formed by the armature 30, the core 33, and the housing 2, and the armature 30 is attracted towards the core 33. The needle valve 12, which moves together with the armature 30, is separated from the valve seat 11, forming a gap, and fuel flows first via the passage grooves 21 in the second end surface 17 of the swirler body 13 through the axial channels 22 in the outer surface 19, flows radially inwards into the rotation grooves 25 in the first end surface 16, flows into the inner annular groove 24 of the first end surface 16 at a tangent thereto and forms a swirling current, then enters the injection hole 10 of the valve seat 11 and is sprayed from the outlet at the tip thereof.
In the fuel injection valve 1 for the cylinder injection constructed in this way, the fastening portion 33d in the flange portion 33c of the core 33, where the core 33 is fastened to the housing 2, is conventionally caulked to prevent the core 33 from being dislodged in the axial direction with respect to the housing 2 due to the high pressure of the fuel flowing therein. In addition, the fastening portion 33d is conventionally welded, etc., around its circumference to increase its strength. The relationship between the forces acting on the fastening portion 33d will now be explained using FIG. 2.
In the figure, letter A indicates the inside diameter (mm) of the inner circumferential surface 2d of the housing 2, into which the external O-ring 40 is, and letter B indicates the inside diameter (mm) of the inner circumferential surface 4a of the delivery pipe 4, into which the delivery pipe O-ring 35 is inserted. The pressure (MPa) of the fuel in the delivery pipe 4 is designated by P.
In the conventional construction for a fuel injection valve for the cylinder injection, A is conventionally greater than B, so that a force of (.pi./4).times.(A.sup.2 -B.sup.2).times.P acts on the fastening portion 33d in the direction of an arrow C. Consequently, the fuel pushes the core 33 in the direction of the arrow C, a direction which loosens the caulking of the fastening portion 33d. As a result, the core 33 is dislodged in the axial direction with respect to the housing 2, which changes the air gap 43 between the end of the armature 30 and the end of the core 33. The problem is that the change in the air gap changes the force of attraction of the solenoid assembly 26 which raises the needle valve 12, which in turn changes the amount of fuel which is injected into the cylinder head 5.
In order to solve the above problem, the dislodgment of the core 33 in the axial direction with respect to the housing 2 has conventionally been prevented by caulking the fastening portion 33d of the core 33, where the core 33 is fastened to the housing 2, and additionally welding, etc., the fastening portion 33d around its circumference to increase its strength, as described above, but the problem is that this requires welding in addition to caulking and leads to increased costs.